feat: NAS storage for invoices/offers, code cleanup, date/time fixes

- NAS storage for created invoices (PDF via puppeteer), received invoices,
  and offers with auto-save on create/edit
- Deterministic file paths derived from DB fields (no file_path column needed)
- Separate NAS mount points: NAS_FINANCIALS_PATH, NAS_OFFERS_PATH
- Invoice language field (cs/en) stored per invoice, replaces lang modal
- Invoices list filtered by month/year matching KPI card selection
- Centralized date helpers (src/utils/date.ts) replacing all .toISOString()
  calls that returned UTC instead of local time
- Attendance project switching uses exact time (not rounded)
- Comment cleanup: removed ~100 unnecessary/Czech comments
- Removed as-any casts in orders and attendance
- Prisma migrations: add invoice language, drop received_invoices BLOB columns

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/routes/admin/sessions.ts

@@ -21,7 +21,6 @@ function parseUserAgent(ua: string | null): {
       icon: "monitor",
     };
 
-  // Browser detection
   let browser = "Neznámý prohlížeč";
   if (ua.includes("Edg/")) browser = "Edge";
   else if (ua.includes("OPR/") || ua.includes("Opera")) browser = "Opera";
@@ -29,7 +28,6 @@ function parseUserAgent(ua: string | null): {
   else if (ua.includes("Safari/") && !ua.includes("Chrome")) browser = "Safari";
   else if (ua.includes("Firefox/")) browser = "Firefox";
 
-  // OS detection
   let os = "Neznámý systém";
   if (ua.includes("Windows")) os = "Windows";
   else if (ua.includes("Mac OS X") || ua.includes("Macintosh")) os = "macOS";
@@ -37,7 +35,6 @@ function parseUserAgent(ua: string | null): {
   else if (ua.includes("Android")) os = "Android";
   else if (ua.includes("iPhone") || ua.includes("iPad")) os = "iOS";
 
-  // Device icon
   let icon = "monitor";
   if (
     ua.includes("Mobile") ||
@@ -76,7 +73,7 @@ export default async function sessionsRoutes(
         is_current: currentHash ? s.token_hash === currentHash : false,
         device_info,
         ip_address: s.ip_address || "",
-        created_at: s.created_at ? s.created_at.toISOString() : "",
+        created_at: s.created_at ?? "",
       };
     });